Method for compression molding plastic articles

ABSTRACT

A method for compression molding plastic articles such as closures include a plurality of tools mounted in opposed pairs with the tools of each pair including opposed male and female mold sections. The tool pairs are mounted for motion in an endless path. The tool pairs and associated mold sections are closed during motion in the path for compression a molding charge in the mold cavity formed between the mold sections of each pair, and opening the mold cavity to release an article formed between the mold sections. A latch mechanism is associated with each pair of tools for holding the tools and mold sections in the closed position during motion in the path independent of the mechanism for closing the tools and mold halves. In this way, forces imparted to the mold halves and tools to hold the mold closed are isolated from the machine frame. The latch mechanism is selectively unlatched to permit opening of the mold halves and release of the article compression-molded between the mold halves.

The application is a division of application Ser. No. 08/857,666 filedMay 16, 1997, now U.S. Pat. No. 5,866,177.

The present invention is directed to a method and apparatus forcompression molding plastic articles such as closures, and moreparticularly to an improvement in the method and apparatus disclosed inU.S. Pat. No. 5,554,327.

BACKGROUND AND OBJECTS OF THE INVENTION

U.S. Pat. No. 5,554,327, assigned to the assignee hereof, discloses amethod and apparatus for compression molding plastic articles such asplastic closures. A plurality of tools are mounted in a circumferentialarray on a rotatable turret in a plurality of opposed coacting pairs.The tools of each pair carry opposed male and female mold sections thattogether. when closed, form a cavity mold for compression molding thedesired articles. The turret is mounted on a machine frame that alsocarries cams for operative engagement with the tools for moving thetools of each pair toward each other during a portion of motion of thetools around the turret axis for compression molding articles betweenthe tool pairs, and for moving the tool pairs away from each otherduring another portion of tooling travel for releasing articles moldedbetween the tools. Fluid Cylinders are associated with each tool pair toprovide a constant limiting molding force for each tool pair. U.S. Pat.No. 5,603,964, also assigned to the assignee hereof. discloses anapparatus for cutting and delivering extruded plastic gobs to thesuccessive molds of the molding apparatus.

Although the methods and apparatuses disclosed in the noted patentsaddress and overcome problems theretofore extant in the art, furtherimprovements remain desirable. For example, it is desirable to hold thetools and mold halves in the closed and compressed position for as longas possible to improve cooling efficiency and part definition andquality during the molding process. However, it is also undesirable toemploy the cams on the machine frame for holding the molds closed atnormal molding force during most of the operating cycle because thiswould place undesirable forces on the machine frame and increase camwear. For this reason, it is conventional practice to reduce mold forcesduring the curing portion of the cycle, with corresponding reduction incooling efficiency and part quality. It is also desirable to improvemachine efficiency by increasing the tooling density within a machine,and thereby increasing overall productivity per unit of plant floorspace. However. employing conventional technology, this would onlyexacerbate the mold force problem, which in turn would require redesignof the machine frame. cams and bearings.

It is therefore a general object of the present invention to provide amethod and apparatus for compression molding plastic articles thatpermit maintenance of full compression force on the mold elements duringthe forming and curing of the molded component while reducing wear onthe cams that close the mold elements, and while reducing mold clampingreaction forces applied to the machine frame. Another object of thepresent invention is to provide a method and apparatus of the describedcharacter that achieve improved efficiency in terms of tooling densityand utilization of plant floor space.

SUMMARY OF THE INVENTION

A method and apparatus for compression molding plastic articles such asclosures in accordance with the present invention include a plurality oftools mounted in opposed pairs with the tools of each pair includingopposed male and female mold sections. The tool pairs are mounted formotion in an endless path. The tool pairs and associated mold sectionsare closed during motion in the path for compression molding a charge inthe mold cavity formed between the mold sections of each pair, andopening the mold cavity to release an article formed between the moldsections. In accordance with one aspect of the present invention, amechanism is associated with each pair of tools for locking the toolsand mold sections in the closed position during motion in the pathindependent of the mechanism for closing the tools and mold halves. Inthis way, forces imparted to the mold halves and tools to hold the moldsclosed are isolated from the machine frame. The locking mechanism isselectively unlocked to permit opening of the mold halves and release ofthe articles compression-molded between the mold halves.

The opposed tool pairs are mounted in the preferred embodiment of theinvention on a slide mechanism that interconnects the tools of eachpair. The locking mechanism is disposed to engage the slide mechanism toprevent motion of the tools of each pair away from each other. The slidemechanism in the preferred embodiment of the invention includes a slideshaft coupled to one of the tools of each pair, with the other tool ofeach pair being slidable on the shaft. The locking mechanism includes astop on the shaft and a latch disposed on the other tool of each pairfor movement between a first position in engagement with the associatedstop for holding the tools and associated mold sections in closedposition, and a second position in non-engagement with the stop forpermitting opening of the tools and associated mold sections. The latchin the preferred embodiment of the invention is urged to the first orlatching position by a spring disposed between the latch and the tool onwhich the latch is mounted, and is moved to the second or non-latchingposition by means of a latch actuator that extends from each latch forengagement with a cam disposed in fixed position on the machine frameadjacent to the path of tool travel. The latch and stop are so contouredwith respect to each other that an increase in molding force within acompression mold cavity increases the force of abutting engagementbetween the latch and the stop.

In accordance with another aspect of the present invention. each of thetool assemblies carries mold cavity cores and holders for forming aplurality of mold cavities at each tool pair. The mold cavities areequally spaced from each other circumferentially of the mold path, bothwithin each tool set and between tool sets. Density of production isthus greatly increased as compared with prior art in which each toolpair forms only a single cavity. The mold elements and cavitiespreferably are disposed in arrays on each tool pair concentric with theturret axis. Preferably, each tooling within each array is equallycircumferentially spaced from its adjacent tooling within the samearray. The mold cavities may be radially aligned or radially staggeredwith the same number of cavities in each array, or may be disposed suchthat there is a greater number of cavities in the outer array than inthe inner array.

BRIEF DESCRIPTION OF THE INVENTION

The invention, together with additional objects, features and advantagesthereof, will be best understood from the following description, theappended claims and the accompanying drawings in which:

FIG. 1 is a sectional view in side elevation of a compression moldingapparatus in accordance with one presently preferred embodiment of theinvention;

FIG. 2 is a top plan view of the molding apparatus illustrated in FIG.1;

FIG. 2A is a fragmentary view on an enlarged scale of a portion of FIG.2;

FIG. 3 is a fragmentary elevational view of a portion of the machineillustrated in FIG. 1 on an enlarged scale;

FIG. 4 is a fragmentary elevational view of another portion of themachine illustrated in FIG. 1 on an enlarged scale;

FIG. 5 is a fragmentary elevational view showing timing of the variouscams in the apparatus cam section;

FIGS. 6A-E are fragmentary elevational views that illustrate the upperand lower tooling assemblies at sequential stages of operation;

FIG. 6F is a view similar to that of FIG. 6D a showing a modifiedembodiment of the invention;

FIG. 7 is an elevational view taken from the direction 7 in FIG. 6E;

FIG. 8 is a fragmentary plan view of the mold charge station in FIG. 2;

FIG. 9 is an elevational view of the mold charge station in FIG. 8 inconjunction with the apparatus tooling of FIG. 3;

FIG. 10 is a fragmentary elevational view similar to that of FIG. 4 butshowing a modified embodiment of the invention;

FIG. 11 is a fragmentary elevational view similar to that of FIG. 5 butshowing modification thereof in accordance with the embodiment of FIG.10;

FIG. 11A is a fragmentary view on an enlarged scale of a portion of FIG.11;

FIG. 12 is a fragmentary elevational view similar to those of FIGS. 4and 10 but showing another modified embodiment of the invention,

FIGS. 13 and 14 are fragmentary views on an enlarged scale thatillustrate respective modifications to the embodiment of FIG. 2;

FIG. 15 is an elevational view of a portion of FIG. 9 showing the gobfeeder disk in greater detail;

FIG. 16 is an elevational view taken substantially from the direction 16in FIG. 2; and

FIGS. 17 and 18 are fragmentary views on enlarged scales of the portionsof the apparatus within the circles 17 and 18 in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The disclosures of above-noted U.S. Pat. Nos. 5,554,327 and 5,603,964are incorporated herein by reference.

FIGS. 1-9 illustrate a compression molding apparatus 10 in accordancewith a presently preferred embodiment of the invention as comprising aturret 12 mounted for rotation about an axis 14 on and with respect to amachine frame 16. Turret 12 has three axially spaced radially extendingplates 18, 20, 22 that form mounting brackets for the compression moldtooling, as will be described. A uniformly spaced circumferential arrayof slide shafts 24 extend parallel to axis 14 of turret 12 through slidebearings 26, 28, 30 carried by turret plates 18, 20, 22 respectively. Anupper tooling assembly 32 includes an upper actuator 34 affixed to slideshaft 24 on opposite axial sides of upper turret plate 18. An upper camfollower roller 36 is carried by actuator 34 for rolling engagement withan upper forming cam 38 carried by machine frame 16 above turret 12.Actuator 34 also carries a roller 40 that cooperates with an upper liftcam 42 on frame 16 for lifting actuator 34 and tooling assembly 32upwardly for release of molded parts. An upper tool holder 44 is carriedby each actuator 34 and slidably mounted on center turret plate 20. Eachtool holder 44 includes an array of mold cores 46 (four in theillustrated embodiment) slidable in associated core sleeves 48 andhaving lower ends that form the male portions of the compression moldcavities. A stripper sleeve 47 (FIGS. 3 and 6-7) surrounds the lower endof each core 46. and is biased downwardly with respect thereto by astripper spring 45 (FIG. 6). Stripper springs 45 are encompassed withinsleeves 48.

A lower tooling assembly 50 includes a slide 52 having axially spacedbearings 54 that slidably embrace shaft 24 between turret plates 20, 22beneath and in opposition to each upper tooling assembly 32. A cavitybracket 56 is mounted on each slide 52. and carries a plurality ofcavity holders 58 (four in the illustrated embodiment) that form thefemale mold sections that oppose cores 46 of the associated upper toolassembly 32 so as to form complete cavities for compression molding ofthe desired articles. Each cavity bracket 56 carries a lower cam roller61 that is disposed for engagement with a lower forming cam 60 carriedby the lower section of machine frame 16. Each cavity bracket 56 alsohas a roller 62 that is engaged by a lower cam 64 carried by frame 16for pulling cavity bracket 56 and slide 52 downwardly, and therebyremoving molded parts from within the mold cavities. Each cavity holder58 is biased upwardly by a spring mechanism. such as a coil spring 65a(FIGS. 1, 3-4 and 6F) or a fluid cylinder 65b (e.g., a nitrogen gasspring, FIGS. 6A-6E). An upper rotary union is mounted to the upperframe and conducts cooling water to the turret and tooling mountedthereon, and is well known in the art of rotary compression molding.

To the extent thus far described, operation of mold apparatus 10 isgenerally as described in above-referenced U.S. Pat. No. 5,554,327. Asturret 12 and tooling assembly pairs 32. 50 move in direction 120 in anendless circular path (FIG. 2) about turret axis 14, mold charges areplaced by a charge mechanism 66 (FIGS. 2 and 8-9) onto cavity holders 58when the cavities are in the open condition illustrated in FIGS. 2 and9. Continued rotation of the turret brings rollers 36, 61 intoengagement with upper and lower forming cams 38, 60, which in turn arecontoured so as to move tooling assemblies 32, 50 toward each other andthereby bring cores 46 into compression cavity-forming engagement withcavity holders 58 and the mold charges placed therein. The toolingassemblies are then held in this closed position as the turret continuesto rotate so as to compression mold and cure the charges placed in themold cavities into articles of the desired contour. In the apparatusdisclosed in the referenced patent, this is accomplished by continuedengagement of rollers 36, 61 with cams 38, 60. As the tools rotate aboutthe turret axis toward the end of the forming cycle, the contours ofcams 38, 60 are such as to release mold pressure on the cavities, andtooling assemblies 32, 50 are moved away from each other by means ofcams 42 64 and cam rollers 40, 62 carried by the upper and lower toolingassemblies respectively. The molded articles are released and strippedfrom the mold tooling, and the tool assemblies are spaced from eachother preparatory to receiving new mold charges.

In accordance with one aspect of the present invention, continued forceis applied to the compression mold elements during the curing cycle by alatch mechanism 70 in conjunction with spring 65a or 65b carried by eachtooling pair and a stop collar 72 disposed at the lower end of eachslide shaft 24. More specifically, each stop collar 72 comprises asleeve 73 that is slidably disposed within each sleeve bearing 30surrounding and affixed to the lower end of each shaft 24. Each sleeve73 has a radially outwardly projecting shoulder 74 at its upper end witha flat radially oriented face, and a lower end in engagement with a ringor collar 76 that affixes collar 72 to shaft 24. As shown in FIG. 18,collar 76 is secured to the lower end of shaft 24 by a screw 77, and issecured to the lower end of stop collar sleeve 73 by the screws 79. Agenerally L-shaped latch 78 is mounted on a pivot pin 80 within a pocket82 at the lower end of each slide 52. A coil spring 84 is captured incompression between a pocket on one leg of latch 78 and an opposing faceof pocket 82 on slide 52. The second leg of latch 78 extends downwardlyfrom pin 80 to a face 88 for opposed abutting engagement with the axialface of stop collar 72. It will be noted that the face 88 of latch 78 isangulated with respect to the longitudinal dimension of the associatedlatch leg so as to be in opposed facing engagement with stop collar 72at the latched position of the latch illustrated in FIG. 4. A latchactuator rod 90 is coupled at one end to each latch 78 by a pivot pin92, and extends downwardly through a bearing 94 on turret plate 22. Asbest seen in FIG. 17, pin 92 extends through a slot 93 in latch 78 toaccommodate pivoting of latch 78 about pivot pin 80. The lower end ofactuator rod 90 carries a cam roller 96 that is disposed for axialengagement with a cam 98 carried by the lower section of machine frame16. A pin 100 is affixed to middle turret plate 20 by a screw 102, andextends downwardly from plate 20 into a pocket 104 formed on slide 52for preventing rotation of slide 52 about shaft 24. An antirotationbracket 103 (FIGS. 1-4) is fastened to each actuator 34. and slidablyembraces the shaft 24 of the next-adjacent tooling pair (see FIGS. 2 and2A) to prevent rotation of each actuator 34 about the axis of itsassociated shaft 24. Screws 102. pins 100 and brackets 103 thus keep thetooling pairs in alignment. Brackets 103 also maintain tangentialalignment of rollers 36 with cam 38.

In operation, when the mold cavities are open in the condition of FIGS.3 and 6A for receiving mold charges. the lower leg of latch 78 is biasedby spring 84 into radial sliding engagement with the outer periphery ofshoulder 74 on stop collar 72. As turret 12 continues to rotate pastmold charge station 66 (FIG. 2), upper and lower rollers 36, 61 areengaged by upper and lower cams 38, 60 as previously described so as toclose the mold sections. As lower tooling assembly 50 and latch 78 aremoved upwardly by cam 60, and as upper tooling assembly 32 and slideshaft 24 are moved downwardly by cam 38, latch 78 slides along theopposing radial surface of stop collar 72 until the end of latch 78clears shoulder 74 of stop collar 72. At this point. latch 78 is urgedby spring 84 to the latched position illustrated in FIG. 3. The forcesapplied by upper cam 38 may now be removed, and the opposed moldsections are clamped in compression molding engagement by operation oflatch 78 against stop collar 72. This clamped condition is thereaftermaintained during a major portion of rotation of the turret and toolsections (FIG. 2) until the tool assemblies again enter cam section 110within which all cams 38, 42, 64, 98 are disposed. Upper cam 38 thenagain applies compressive forces so as to release latch 78 for movement.At this point, cam roller 96 is brought into engagement with latchrelease cam 98 (FIGS. 1, 3 and 5), which moves actuator rod 90 upwardlyand pivots latch 78 out of engagement with stop collar 72. With thelatch thus held by cam 98 and actuator rod 90 out of the latchingposition, the camming forces on upper roller 36 and lower roller 61 maybe released, and rollers 40, 62 are brought into engagement with cams42, 64 for separating the mold halves. Thus, the particular tool pair isready for a next charge and mold cycle.

FIG. 5 illustrates timing of cams 38, 42, 60, 64 an 98 within camsection 110. With the mold tooling passing through the cam section inthe direction 120, mold charges 121 (FIG. 6A) are loaded into the moldcavities during the path portion 122 (FIGS. 5 and 6A) in which the moldtooling assemblies are held apart by cams 42, 64 in cooperation withrollers 40, 62. After the mold cavities are charged, continued rotationof the turret in direction 120 causes lower tooling assembly 50 to belifted by lower forming cam 60 in path portion 124 (FIGS. 5 and 6B). Asthe lower tooling assembly continues to move upward, latch 78 is insliding contact with the side of stop collar 72 for the full upwardstroke of the lower tooling. Cavity holders 58 contact stripper sleeves47 and force the stripper sleeves upward against stripper sleeve springs45 to close the mold cavities. Upper tooling assembly 32 is then loweredin path portion 126 (FIGS. 5 and 6C), by operation of cam 38 and roller36, by a fixed stroke determined by cam 38. Toward the end of thisstroke, the mold limiting force is reached and cavity holders 56 arecompressed against the force limiting mechanism provided by eithernitrogen gas cylinders 65b or coil springs 65a. At this time, the forceof molding results in a reaction force against the cavity and its cavityholder 56 through the nitrogen cylinder or spring, and is opposed bylower forming cam 60. Further actuation of the upper actuator to itsfinal extended position at path portion 128 (FIG. 5) causes cavityholder 56 to move further downward relative to lower actuator slide 52,further compressing the fluid or coil spring, which limits the moldforce. At this relative position of upper actuator shaft 24 and slidelatch 78, latch 78 clears stop collar 72. and latch spring 84 causes thelatch to move into place above the stop collar. As the toolingprogresses from upper forming cam 38 at path portion 130 (FIG. 5), theupper tooling assembly is raised by the upward force of the nitrogen orcoil spring until latch 78 contacts the upper surface of stop collar 72,which prevents any further separation of the upper and lower toolingassemblies. At this point, the whole lower tooling assembly 32 and 50 isheld in a downward position against the reaction force of strippersprings 45, and opposed by lower cam 60 against roller 61.

The tooling assemblies are thus held in a compressed state for theremaining rotation of the turret (FIG. 2) during curing by operation ofthe latching device, with minimal force being applied to the lower camand the upper cam being entirely absent. The tooling assembly is thusself-locking. and the opposing forces of the upper and lower toolingassemblies are contained within the tooling assembly, resulting in onlythe stripper spring force exerting external force against the machineframe. This force is approximately 30% of the total mold force, and isapplied in a downward direction against the lower cam and resisted bythe turret assembly. As turret rotation continues along path portion 131into cam section 110 following the cure cycle, upper rollers 36 aresequentially brought into engagement with a releasing section of uppercam 38, which slightly compresses the nitrogen or coil mold forcelimiting springs so as to relieve the force applied to latch 78. Whilethe latching force is so relieved, roller 96 on latch actuator rod 90 isbrought into engagement with cam 98, which releases the latch mechanismand holds the latch mechanism open when lower cam 64 is brought intoengagement with rollers 62 at time 132 for lowering the lower toolingassembly. The lower tooling assembly is thus lowered at path portion 134(FIGS. 5 and 6D), at which point cam 98 can release latch actuator rod90. The upper tooling assembly may then be released at time 136, andmoved upwardly by cam 42 and roller 40 for stripping formed parts fromcores 46 between the tooling assemblies (FIG. 6E) preparatory to loadingnew mold charges.

FIGS. 8, 9 and 15 schematically illustrate mold charge station 66. Amold pellet wheel assembly 140 has an inner angularly spacedcircumferential array of charge pellet transfer cups or nests 142 and anouter angularly spaced circumferential array of charge pellet transfercups or nests 144. The arrays of nests 142. 144 are disposed onrespective radially adjacent annular wheel sections 146, 148. Section148 is circumferentially slidably carried by section 146. Sections 146,148 are fastened to each other by screws extending through slotted holes(not shown). FIG. 9 is a schematic representation of wheel 140 havingtwo nests 142, 144 in alignment with a pair of mold charge nozzles 150,152 on a nozzle block 158, and a diametrically opposed pair of nests142, 144 overlying the mold cavities 59 into which the mold charges arebeing positioned. Nozzles 150, 152 are connected to dedicated chargemelt channels 154, 156 within nozzle block 158. These channels areindependently supplied with extrudate from a source 160 at a rateproportional to the angular velocity of turret 12. For radially alignedmold cavities as illustrated in FIG. 2, the two cavities may be loadedsimultaneously. The trailing radially aligned cavities in four-cavitytooling of the type illustrated will receive their mold materials at anincrement in time later than the leading cavities within the four-cavitycluster. This time difference is not significant within the overallcycle time. Two pellet cups or nests 142, 144 simultaneously align withtwo cavities 59 within lower tooling assembly 50. As pellet wheel 140continues to rotate, an adjacent pair of pellet cups move into alignmentwith the remaining two cavities within the cluster, and pellets aredischarged into the cavities. Since the instantaneous speed of pelletcup 144 is greater than that of pellet cup 142, the trajectory of therespective pellets from each will have a different path toward theunderlying cavity. Furthermore, the cavity coincident with pellet cup144 will be moving at an instantaneous speed somewhat less than thecavity associated with cup 142.

For this reason, outer ring 148 can be mechanically circumferentiallyadjusted with respect to inner ring 146 to compensate for such speeddifferences.

In accordance with one aspect of the present invention, the moldcavities are provided in arrays that travel in an endless path,preferably a circular path, in equally circumferentially spaced arrays.Thus, in FIG. 2, there is an inner circular array of mold cavities 59and an outer circular array of mold cavities 59, with two cavities ofeach array being disposed in each tooling pair. That is, each toolingpair holds two cavities of the inner array and two cavities of the outerarray, or a total of four cavities. It will be noted in particular thatthe cavities 59 of the inner array and the cavities 59 of the outerarray are uniformly and equally spaced from each other both within eachcavity bracket 56 and between adjacent cavity brackets. Likewise, thecharge transfer cups or nests 142 and 144 in transfer wheel 140 (FIGS.8-9 and 15) are provided in equally spaced circumferential arrays. Thus,angular velocity of wheel 140 is coordinated with angular velocity ofturret 12 so that each may rotate continuously and at constant speedduring operation. As noted above, outer ring 148 is circumferentiallyadjustable with respect to inner ring 146 for timing dispensation ofmold charges from the inner and outer cups. In the alternativeembodiment of FIG. 13, the number of mold transfer cups or nests 142within inner ring 146 may be reduced by one-half. or source 160 may betimed to deliver extrudate to every other inner nest 142. However, wheel140 will still rotate at constant angular velocity, and outer ring 148may be readily adjusted to accommodate the offset disposition of themold cavities in FIG. 13. The mechanism for delivering the mold chargesto the disk transfer nests and from the disk transfer nests to the moldcavities is the same as in above-referenced U.S. Pat. No. 5.603,964.

FIG. 7 illustrates T-slot connection between core pins 46 and actuator34 of each upper tooling assembly 32. Two T-slots 34a, 34b in eachactuator 34 locate all four core pins 46 within each tooling assemblycluster, each slot being of sufficient width to accommodate the linearpitch difference between cores in the inner array and those in the outerarray. By this means, the complete tool holder assembly 44 can bequickly removed from the machine for maintenance or repair. It will alsobe recognized that, although a cluster of four cavities for each toolassembly pair is illustrated in the drawings, the principles of thepresent invention in their broadest aspects are not necessarily solimited. Each actuator pair could handle one much larger part, or acluster of three cavities in which the number of cavities in the outerarray would be twice that in the inner array. Since the delivery path toeach nozzle 50, 52 (FIG. 9) is independently controlled, the gram weightof the pellets received by the cavities in the inner array can differfrom those received in the outer array. Consequently, parts of adifferent size and shape can be manufactured in the inner and outerarrays.

Implementation of the invention as illustrated in FIGS. 1-9 reducesmachine loading approximately 90% as compared with the prior art becausefewer tools are simultaneously under compression from the forming cams.Although full mold pressure is applied at all tools during the curecycle, only the forces applied by the stripper sleeve springs areresisted by the lower forming cam. All other forces are contained withinthe tooling by the latch mechanism, and these are isolated from themachine frame. There is a considerable reduction in forces (on the orderof about 70%) applied to the lower forming cam during the cure cycle,and a 100% reduction in forces applied to the upper forming cam. Simplystated, the upper forming cam is needed only during the opening andclosing stages of the mold tooling (FIG. 5). As the number of machinecavities increases, this feature of the invention becomes increasinglysignificant.

FIGS. 10. 11 and 11A illustrate a modified apparatus 10a in accordancewith an alternative embodiment of the invention, in which the need toextend the lower lift cam entirely around the apparatus is eliminated.Specifically, an annular tool support ring 141 is rigidly mounted by aseries of support pillars 143 affixed beneath ring 22 of turret 12.Support ring 141 carries an array of circumferentially spaced collars145 that align in assembly with the lower ends of the several toolingshafts 24. The axial lengths of collars 145 are selected so as toreceive the ends of shaft 24 and abut the axially lower face of rings 76that affix stop collars 74 to shafts 24. Support ring 141 and collars145 thus limit downward motion of these several actuator shafts 24, andresist the reaction force of mold stripper springs 45 (FIG. 6) that pushdownward on the lower actuator and the latch mechanism, which transfersthe force to actuator shaft 24 when the tooling is in the latched mode.The embodiment of FIGS. 10, 11 and 11A increases stresses within theturret, but eliminates the stress load on the turret bearings.Furthermore. the need for extending the lower cam entirely around thepath of travel is eliminated, so that lower cam 60a is disposed entirelywithin cam section 110a, as are the other cams. As shown in FIG. 11A,lower cam 60a embodies a rise 60b that is timed in associated with cam98 so as to lift lower actuators 56 and relieved forces on the latchmechanisms as the latches are released by cam 98. Clearly, by choosingappropriate profiles on upper cam 38 and lower cam 60, the latch releasecould be accomplished by the action of the upper cam as previouslydescribed, and this alternative description of function is not intendedto limit such earlier embodiment.

FIG. 12 illustrates another modified apparatus 10b in accordance withthe present invention, in which the need to extend the lower lift camentirely around the apparatus again is eliminated. A stop plate 150 ismounted on each upper actuator 34 overlying turret plate 18, and a stoppad 152 is disposed on plate 18 beneath each stop plate 150. As upperactuator 34 and upper tooling assembly 32 is moved downward by camroller 36 to the latched position, stop plate 150 and stop pad 152cooperate to limit such downward motion. When the latch is actuated, theforces of stripper springs 45 (FIG. 6) are transferred to upper turretplate 18 actuator 34, stop plate 150 and stop pad 152. The need for thelower cam entirely around the path of travel is thus eliminated,although increased loading is placed on securement of upper actuator 34to shaft 24. In each case of alternative methods of eliminating lowercam 60 in the curing portion of the cycle, an appropriate ramp downwardon cam 60 would be required to allow the latched tooling assembly 32, 56to be lowered onto the respective stops 150, 152 or 144. 140 in acontrolled manner.

FIG. 13 illustrates a modification to the preferred embodimentparticularly as shown in FIG. 2, whereby each upper and lower toolassembly carries tooling for three rather than four mold cavities. Morespecifically, the upper and lower tooling assemblies carry mold cavityholders 58a, mold cores 46, core sleeves, etc for three mold cavities.There are thus two concentric array of mold toolings, with the outerarrays having twice as many cavities as the inner array. FIG. 14 shows amodification in which the multiple mold cavities in each toolingassembly is replaced by single cavity tooling 56b, 58b of largerdiameter.

The following description relates to alternative means for providing aselectable restraining of opposing movement of the tooling pairs 32 and50 and is included to illustrate that the above-mentioned locking meanscan be achieved by alternate means, and as such the application is notlimited to the preferred means illustrated in the figures. For example,in a first modified form of the invention, referring to FIG. 3, slide 52and upper actuator 34 could be connected by a hydraulic cylinder, withthe cylinder rod attached to actuator 34 and the cylinder body isattached to slide 52 in a parallel relationship to the turret axis. Thecylinder stroke is fixed and the hydraulic pressure controlled such thatthe tooling closed condition is sufficient to ensure compression of thepellet and forming of the article, and the molding force is limited bythe spring means in the lower actuator, whereby the hydraulic forcesexerted by the cylinder marginally exceeds the force required tocompress the spring means in the lower actuator. A rotary union could beattached for example to the machine base, and mounted coaxially with theturret from a static hydraulic power unit mounted to the machine base.By conducting the pressurized oil to a plurality of mechanicallyactuated four-way hydraulic valves, each associated with one of each ofan equal number of said hydraulic cylinders and mounted to the turret,it is possible remotely to actuate the valves by a static cam on themachine base selectively to actuate the cylinders and power the toolingpairs to a closed position or to an open position. Using this method,upper cam 36 and/or lower cam 60 could be used to ensure that therelative axial position of the pairs of mold assemblies relative to theturret are in a controlled path during the closing and opening of themold by the actuation of the cylinders, This method would providelocking means to hold the opposing toolings closed independent ofexternal cams, and as such would function as a locking feature asdescribed in the preferred form of the invention, and in addition couldprovide the actuating force to close the molds.

In another form of the invention, a hydraulic cylinder could be usedwithout the need for an externally mounted hydraulic power supply. Inthis case, each cylinder as described above preferably would have athrough rod such that the annular area of the piston would be equal tothat of the opposing side of the cylinder. A two-way mechanicallyactuated valve, positioned as described in the first modified form ofthe invention, would be connected to each of the two cylinder ports,such that with the valve in the open condition, as the piston isdisplaced, the oil contained within the cylinder on one side of thepiston can transfer to the opposite side of the piston passing throughthe open valve. As both sides of the piston are preferably of equalarea, the total volume of oil within the cylinder remains constant andno make-up oil is required. Conversely, if the valve is held closed,then oil cannot transfer rom one side of the piston to the opposing sideand the piston is effectively locked in position and the opposingtoolings cannot move axially relative to each other. By causing themechanically actuated valve to be actuated to an open condition, thetooling would be controlled by the cams as mentioned in the preferredmethod such that the toolings can be opened and closed with littleresistance. Conversely, when the toolings transfer to the curing portionof the cycle having no cams, the valve is spring biased to its freestate, and the valve will be closed causing the toolings to be locked inan axial relationship as at the time of closing the valve. This wouldsubstantially replicate the condition as described in the preferredmethod, effectively locking the opposing toolings in a fixed axialrelationship to hold the opposing toolings closed independent ofexternal cams, and as such would function as a locking feature asdescribed in the preferred form of the invention.

In another form of the invention, the movement of actuator 34 attachedto shaft 24 relative to slide 56 can be selectively limited by a fluidpressure actuated shaft clamp. This clamp is rigidly attached to theslide and comprises a pair of semi-cylindrical clamp shoes. A hydraulicactuating cylinder compresses the shoes to the shaft and provides africtional hold to the shaft relative to the slide. Actuating means forthe hydraulic cylinder would be according to the above-described firstmodified form of the invention. In this case the cam actuating thehydraulic valve would provide selective clamping of the said shaft, toprovide a locking means to prevent relative movement of actuator 34 toslide 56. Thus it can be understood that this form of the inventionprovides an alternative means to that of mechanical latching means ofthe preferred form of the invention.

A further form of the invention utilizes a ball screw and ball nut,along with a mechanical clutch brake. Said clutch brake being springloaded to the brake condition and mechanically actuated to the freecondition. In this case, the ball screw is rigidly attached to anextension of upper actuator bracket 34 by means of a shaft bushing keyedand axially secured to the ball screw. and this bushing is secured toactuator bracket 34 by securing screws. Thus, the ball screw is held ina fixed relationship to actuator 34, and is mounted parallel to the axisof the turret, Slide 52 has a corresponding ball nut bearing mountedcoaxially with the ball screw within the slide for rotational relativemovement with the slide, but is restrained from axial movement relativeto the slide. Further, a mechanical clutch brake is mounted to the ballnut and to the slide such that in its spring maintained condition, thebrake is applied to provide rotational restraint to the ball screw withrespect to the slide. The clutch brake is actuated by a remote cam in asimilar manner to that operating the latch release in the preferred formof the invention, and in this case will operate to oppose the clutchspring and to allow the ball nut to rotate. It can be understood fromthis description that the ball screw can move axially relative to theslide only during the period that the brake is disengaged, whereby theball nut is free to rotate as it is driven by the advancing orretracting ball screw. However, during the period when the brake isengaged, the ball nut cannot rotate relative to the slide, and axialmovement of the ball screw relative to the slide is inhibited. This formof the invention provides a further alternative to the latching meansdescribed in the preferred form of the invention.

What is claimed is:
 1. A method of compression molding plastic articlesthat comprises the steps of:(a) providing a plurality of tool meansmounted in opposed pairs, with the tool means of each pair both beingmoveable toward and away from each other, and with the tool means ofeach pair including opposed male and female mold means, (b) moving thetool means pairs in an endless path with respect to a machine frame, (c)positioning first cams on the machine frame for closing the tool meansof each pair by moving both of said tool means toward each other to aclosed position during a first portion of motion of said tool means insaid endless path for compression molding mold charges between thepairs, and for opening said tool means by moving both of said tool meansaway from each other during a second portion of motion of said toolmeans in said endless path for releasing molded articles, (d) lockingsaid tool means of each pair to each other in said closed position by:(d1) mounting a latch mechanism on each said pair of tool means and alatch actuator extending from each said latch mechanism, and (d2) movingsaid latch mechanism to lock the tool means of each pair to each otherwhen said tool means pair is moved to said closed position so as toisolate from the machine frame forces imparted to said tool means tohold said tool means together during compression molding in said step(c), and (e) unlocking said tool means of each pair from each other by:(e1) positioning a second cam on the machine frame separate from thetool means for engagement with the latch actuator of each said toolmeans pair, and (e2) moving the latch actuator of each pair by engagingsaid latch actuator with said second cam to release said latch mechanismand permit opening of said tool means pair by said first cam as saidtool means pair enters said second portion of motion in said endlesspath.
 2. A method of compression molding plastic articles that comprisesthe steps of:(a) providing a plurality of tool means mounted in opposedpairs, with the tool means of each pair including laterally spaced moldmeans forming at least two spaced mold cavities, (b) continuously movingsaid tool means in an endless path, (c) sequentially opening and closingsaid tool means during motion in said path to release molded articlesand receive mold charges, and to compression mold the mold charges toform the articles, and (d) while the tool means are open, deliveringmold charges to said mold means by: (d1) mounting a disk to rotate aboutan axis adjacent to said path such that a periphery of said disk rotatesbetween the tool means when the tool means are open, (d2) providing atleast two concentrically spaced arrays of mold charge transfer means onsaid disk periphery, with said arrays being radially spaced from eachother by a distance corresponding to lateral spacing between said moldmeans on each said tool means such that said mold charges are deliveredto said laterally spaced mold means simultaneously by saidconcentrically spaced arrays of mold charge transfer means, (d3)continuously rotating said disk in synchronization with said tool meansin said path, and (d4) mechanically adjusting the of said concentricallyspaced arrays of transfer means circumferentially with respect to eachother for timing delivery of mold charges to said mold means.
 3. Themethod set forth in claim 2 wherein said step (d3) comprises the step ofrotating said disk at a fixed ratio to motion of said mold means in saidendless path.